Event-related brain potentials (ERPs) of 13-21-year-old autistic subjects and age-matched controls were elicited by auditory stimuli in a variation of orienting response paradigms. Unexpected, novel sounds (bizarre concoctions of human, mechanical and computer sounds) were randomly inserted as probes in a sequence of expected, non-novel sounds (the word 'me'). In order to help ensure that both subject groups were attending to this stream of information, each subject was required to press a button to a specified target sound (the word 'you') also randomly inserted in the sequence of expected non-novel sounds. The ERP results showed that in both groups, unexpected, novel probes and also targets evoked a different neurophysiological response than did expected, non-novel sounds. This suggests that the autistic group did not misperceive novel information as non-novel and were able to make simple classification decisions as accurately as normal controls. However, in the autistic group, there may be less 'processing' of the novel probes and of targets: compared to the control group, the autistic group had smaller amplitudes of two long-latency components to novels and smaller P3b amplitudes to targets. The two components to novels were termed A/Pcz/300 (A = auditory; P = positive; cz = electrode site of maximum amplitude; 300 = latency in msec) and A/Ncz/800. In another sequence of sounds, subjects simply listened to frequently presented 'me' sounds (90%) and infrequently presented 'you' sounds (10%). In this no-task condition, no differences between autistic and normal control subjects were found.